This invention relates to a method for handling a work in a robot system, especially a method for teaching a holding position of the work and a holding angle of a hand holding the work at the holding position in the robot system having a visual sensor.
In a robot system like an industrial robot, first, a man directly or indirectly teaches operations to the robot in a teaching mode or a training mode, so that the operations are entered into the memory of the robot system. Then, the robot reproduces the memorized operations for actual processing. Accordingly, for example, in the case of handling works, parts, or objects, the work to be handled has to be exactly positioned at the place determined in the teaching mode. Usually, however, it is very difficult to do so.
In order to resolve such a problem, conventional methods attach a visual sensor to the robot so as to recognize the position, the direction or the orientation and the shape of the work and handle it by using these data. It is comparatively easy to handle the work, if it lies within the visual field of the visual sensor.
Such a robot system is disclosed in some technical papers, for example, Gerald J. Agin: "Computer Vision Systems for Industrial Inspection and Assembly", COMPUTER, May, 1980, pp. 11 to 20.
Generally, in the robot system having the visual sensor, there are a visual coordinate, a robot coordinate and a hand coordinate, which are usually different from each other. Further, the holding position of the work and the holding angle of the hand holding the work, which is initially held by the hand of the robot, inherently depend on each work. Therefore, in the case of moving the robot by using measured data of the visual sensor, it is necessary to acquire in advance the mutual relations between all of the coordinates, the holding position of the work and the holding angle of the hand holding the work.
There are some methods for obtaining the mutual relations between all of the coordinates in the prior art. For example, the Japanese Laid Open Patent Application No. 58-114887, laid open on July 8, 1983, discloses a method using two marks attached to the work. Namely, the positions of the marks within the visual field are input by the visual sensor, and the mutual relations are determined by using the position data of the two marks and the posture data of the robot. In this method, however, it is necessary to know the exact positions of two marks on the work in advance. Further, this prior art does not disclose how to acquire the holding position and the holding angle of the work, because, this prior art is made on the assumption that the shape of the work is a square.